1. Field of the Invention
The present invention relates to a surface acoustic wave device.
2. Description of Related Art
Surface acoustic wave devices have been widely used such as for filters in communication and other fields. They find a particular use in a mobile radio communication field for their simple constructions effective in providing satisfactory characteristics. In such a mobile radio communication field, an increasing demand has arisen for their operations at higher frequencies with recent increase in information contents. Consequently, the surface acoustic wave devices have been mostly operated in the UHF range.
One method of achieving high frequency operations of the surface acoustic wave devices is to improve electrode constructions such that an electrode period thereof can be reduced. Another method contemplates to laminate upon a piezoelectric substrate a surface wave propagation film which allows high-speed propagation of acoustic waves.
Japanese Patent Laying-Open No. Hei 1-17795 (1989) discloses a diamond thin film for use as the surface wave propagation film which allows high-speed propagation of acoustic waves.
However, if such a diamond thin film is to be formed, a substrate needs to be heated generally to 800-900.degree. C. This causes a high degree of heat stress in the laminate to disadvantageously result in poor adherence thereof to an underlying layer.
Also, the high temperature film-forming accompanies complicated fabrication processes. The influence of heat upon the underlying layer including the substrate must be taken into consideration. This, for example, makes it difficult to form the diamond thin film subsequently to the formation of electrodes such as of aluminum.